1. Field of the Invention
The present invention concerns an interferometric device for detecting the presence of gas and concerns, in particular, a highly sensitive device allowing the analysis of several gases.
2. Summary of the Prior Art
Interferometric devices for the analysis and/or distribution of gas or the identification of these gases are known.
A birefrigerent plate between two polarizing elements associated with an interferential filter are utilized as interferometric means, these means being provided so as to adjust the thickness of the birefrigerant plate thereby adjusting the path difference introduced by this plate. Effect is made, for example, of the controlled temperature of this plate.
One of the polarizing elements is rotated in order to ensure the modulation of the system at the output of which is disposed a detector supplying a signal during analysis.
Thus, in a prior art device, the image of a light source emitting in the ultraviolet range is formed on the detector, through a cell containing the gas to be analyzed and the interferometric and modulation means described hereinabove.
Such a device, utilizing as polarizing elements the polarizing films, for example, "Polaroid.RTM.", one of which rotates, is perfectly adapted for measuring the emission. However, it is desirable to use a device presenting a greater sensitivity and, furthermore, which can be utilized without requiring any modification for the detection of several gases.
Therefore, in the prior art devices, certain of the components offer relatively poor performances. The polarizers, in particular, to the extent that they are constituted by polarizing films, have a relatively high absorption rate and a poor extinction rate.
Furthermore, the interferential filter utilized in the prior art device has the drawback of presenting, in the ultraviolet range, a very low transmission rate, of 10 to 15%, and also of allowing a considerable amount of stray light to pass. This stray light creates a noise which can drown out the weak signals.